1) If I'm constructing a building and its not finished, if I decide to cancel the building do I get my cash back?

2) Do I get cash back after demolishing an already established building?

3) I need more friends add me biggrin *Google+ Players only*

blaugh

You won't get your cash back. Once bought, you've lost your cash. So if you don't like the building at the moment, just put it in storage? It would be a waste of your gold pastries to simply destroy it.
Btw you can't cancel a building half-way. Once it's there/built/under construction you can't change your mind anymore.